Process for compounding rubber



Patented Feb. 28, 1933 urrs-n stares PA E FF CE 1 WILLIAM s. oenoorr ANDwiLLrAM A. nonennssg'or rnmvs enovn, new. .rnnsnv, AND

OLIVER M. r-ravnn v, or WILMINGTON,DELAWARE,ASSIGNORS1TO n. I. nix-PourDE NEZMOUBS & COMPANY, WILMINGTGN,

PROCESS FOR COMPQUNDING RUBBER ,No Drawing.

well as sulfur or other vnlcanizing agent, to gether with theaccelerators, anti-oxidants,

and softeners. The incorporation of these materials intorubber has beenaccomplished milling with the plastic unvulcanized rub her. Thisoperation is expensive, and theresults as a rule have not beensatisfactory,

since, even on long milling, the dispersion has not been uniform, whileexcessive milling materially reduces the" quality of the rubber. Variousmethods have been suggested and practiced by those skilled in the art ofrubber compounding. For example, in the mixing of high carbon blackcontent stocks, s'uchas are used for tire treads, stearic acld has beenadded on the mill to assist in the dispersion. Masterbatching and hightemperature milling are other methods which have been'particularlyuseful. Loomis and Stump, in U. S. Patent 1,558,-. 688, havedescribed aprocess which consists in preparing compounding jingredients'fforsubsequent addition to abody of rubber which consists in surrounding andencasing the particles of such ingredients in thin coating of rubber andthen introducing the so treated ingredients into a main body of rubbermaterials. It is well knownthat clay is difiicult to disperse uniformly,in rubber by the ordinary methods, and the method above, as described inU. S. Patent 1,558,688, illustrates one which has been suggested for theimprovement of the dispersion. When dry clay which isa typical lyopholiccolloid, is suspended in water the particles are reduced to coiloi laldimensions. It has been found that the tormationof aniline black by theoxidation of aniline results in a surface film on the clay whichmaterially assists in the dispersion of the 'claj, in'rubber..j Anilineblack itself an ears to be easil incorporated into rubber and theimprovement in dispersion of;

Application filed December is; 1927.: seiirno. 239,810.

the treated clay-is undoubtedly due tethe effect "of the surface film,Bridgwater'and Powers, in U. S; Patent I 1,628,528, describe a method ofuniformly impregnating a mass comprising rubber with finely divided antiaging' compound, the particles of-which tend to adhere, by first offe'cting'an intimate mixture ofsaid compound DE-IiAWARE, A ooarone'rroivorrnnm with a dust adapted to coat the particles I thereof andsubsequently adding the-mixture to the main body of rubber materials.This method consisting in'the simultaneous grind- Y ing'of ananti-"aging compound and an inert diluent, appears to"largely preventthis aggregation of particles'and islcon'sequently a distinctimprovement over the use of an anti-f aging compound, ground by-itself.It has v the disadvantage, however, that the reduc} tion in size of theparticles is dependent upon themechanical means employed; Amicroscopicvexamination of the material prepared according to the" methodof'BridgWater and Powers showed that the dispersion Was-su'pe-I rior topara-amino phenol ground alone, but decidedly inferior to the method inwhich the particles of para-amino phenol'were reduced to colloidal sizeby precipitation. f Y. This invention has as-anobject-the prepa-f rationand conditioning of compoundingingredients to j render them. moresuitable for I incorporation into rubber. I A further object of theinvention is theformation in a colloidal systemof colloidal sizedparticles of- .the compounding ingredientin the presence of anagentwhich tends topreserve the col- 'loida'l nature of the system. Astillfurther object of the invention is the utilization ofan agent forprotectingthe colloidal nature of the compounding ingredients in themedium in which it is formed that functions as a dispersive andasaprotective agent; A final object of'the invention is'incorporation ofthe'pre-treated compounding ingredient into rubber and the dispersingo'fthe compounding ingredientsuniformly throughout the rubber withoutthe necessity of milling. l

,These objects are accomplished by the 01 lowing invention in which thevariousmaterials to be compounded into rubber are first reduced toparticlesof colloidaldiinensions stood that these are illustrative onlyand are not to be taken as limiting our invention:

E mamplc 1.10.9 grams para-amino phenol were dissolved in 100 cc. water,and cc.

' of concentrated HCl. This solution of paraamino phenol hydrochloridewas added all at once to a suspension of 2814 grams stearic' acid and200 cc. of water and 2 5 cc. of. con-- centrated ammonium hydroxide withe-fficient agitation. After filtering,the material was dried andcompounded in the proportion ofl part of product to 100, parts ofrubber.A

thin section ofthis' rubber mixtures was ex v a mined under themicroscope. It was found that thepara-amino phenol particles had beenreduced to such small dimensions. that they were invisible under amagnificationof 440 diameters. For comparison, a similar mixture of 1part of para-amino phenol, which had, been" ground for 24'h0u'rs in aball mill, in parts of. rubber was examinedunder the same magnification.The mixture prepared accordingto the last described method containedparticles of varying size showing that even this prolonged period ofgrinding didnot result in a suflicient reduction in particle size topermit of gooddispersion during the subsequent milling. There'was atendencyfor the finely ground. para-amino phenol to aggregate.

Example 2.As another example illustrating this invention, 100 grams ofpara amino phenol were dissolved-in 400 cc. of water and 76 cc. ofconcentrated HCl. This solution was added all at once to a solution of111 grams of N'a SABI-I O in 300 cc. water, to which had been added29.3: grams sulfur.

The precipitate was filtered off, dried, and.

incorporated into rubber according to the procedure described above. Amicroscopic examination of thin sections of this rubber showed-aconsiderable improvement in efiiciency of dispersion-over that of groundparaamino phenol. 7

Emamplc 3.-lV[eta-toluylene diamine has also been found todisperse-poorly in rubber even after prolonged grinding.- Fifty gramsmeta-toluylene diamine, 50 grams glucose, and 30 cc. water'were heatedwith agitation for 30 minutes. During this time practically all of thewater which had been added evaporated and the boiling point increased to126 C. This material was cast, and 1 gram incorporated into 100 grams ofrubber by milling. Aniicroscopic examination of-a thin section showed noparticles visible under magnificationof 440diameters. a

E mamplc A-As another illustrative example, 50 grams m-toluylene diamineand 50 grams stearic acid were melted together and this mixture cooledpractically instantaneously in thin layers. Under these conditionsmeta-toluylene diamine solidified in particles of colloidal dimensions,as shown by a microscopic examination of a thin section of rubber towhich 1 part of this material had been incorporated. To illustrate thedifference resulting from this pretreatment of the mtoluylene diamine,an equivalent amount of m-toluylene diamine and stearic acid was addedseparately to the mill. The examination under the microscope indicatedthat the particles were not reduced in size during the milling. V 1 p Ewamplc 5.As a further example illustrating the present invention, analcoholic solution containing 10 grams oftetra-methylthiuram-mono-sulphide was added to 40 grams molten stearicacid and 5 cc. concen trated ammonium hydroxide. After the evaporationofthe alcohol, and cooling of the mixture a stearic acid-soap mixture wasvobtained. A thin section of rubber,in which 2.5 grams of thismixture hadbeen milled into 100 grams pale crepe, was compared micro Scopicallywith a thin section containing 0.5 gramtetra-methyl-thiuram-mono-sulphide in 100 grams pale crepe. The lattershowed the unbroken characteristic crystals of the accelerator while thestearic acid-soap mixture containing the same amount of acceleratorshowed practicallyno crystals. 1

It willbe obvious that the process of the invention may be applied to amixture of one or more anti-aging compounds of thetype described. Thus,the use of a colloidal system containing a mixture ofphenyl-alpha-naphthylamine and meta-toluyene-diamine together withstearic acid has been found to be of advantage in cases where it isdesired to impart to the rubber the peculiar anti-aging propertiesinherent in each of these substances.

Uniformly andfinely divided fillers, rein.-,

forcing agents, accelerators and antioxidants have-been so generallyused by those skilled in the art of rubber compounding that the reasonsfor the. insistance 011 this fine state of subdivision need not be givenhere. Many of these materials diificult to disperse by ordinary meanshave, during some stage of their preparation for use in rubbercompounding, existed, or might havebeen made to exist, as particles ofcolloidal dimensions. As an-ex- 'ample, clay in the presence of water,exists as a colloidal suspension, but on removing the water, the clayloses its colloidalproperties. Ifthis dried clay be suspended inbenzene, the system has the properties of a coarse mechanical suspensionand not those of a colloid'al solution or colloidal suspension. If

thesame clay be again suspended in water,

the clay again reverts to colloidal solution. This illustration is givento demonstrate the necessity for the consideration of the effect of thesecond component of the system uponthecolloidal properties of amaterial. Clay can not be said, therefore, to possess inherentlycolloidal properties. Reference has been made to the reduction ofparticles of colloidal dimensions. A colloidal system, asreferred to, inthis patent, may be defined 'as'one con taining definite particles,visible under the ultra microscope, which exhibits Brownian movement.The system is sensitive to ions in solution and the apparent solubilitydepends on the previous history of the sample rather than being afixedvalue' at a given temperature in a given solute.

' Thesteps involved in the application of this invention are enumeratedbelow:

1. Formation in a colloidal system ofcolloidal sized particles of acompounding in-Y gredient for rubber in the presence of adispersing-agent which tendsgto preserve the colloidal nature of thesystem. T 2. Conditioning the compounding ingredient prior tohicorporation into rubber, such as drying, etc. 7 i i i 3. Incorporationof the pie-treated compounding ingredient intorubber at which time theagent which protected the colloidal nature of the compounding ingredientin the medium in which it is formed, functions as a dispersive as wellas a protective agent.

The term compounding ingredient is used above in its broadest sensereferring to any material which may bemiXed with rubber in making acommercial article and includes the so-called fillers, reinforcingagents, vulcanizing agents, accelerators, and antioxidants.

Any method which will result in the formation of colloidal sizedparticles will suiiice (and the process of accomplishing this is not perse the present invention). For example,

the mere agitation of clay with water results in a colloidal suspension.Para-amino phenol, when precipitated from solutions of its salts byalkali'under certain carefully controlled conditions, as described inExample 1', forms a'colloidal solution in water. Rapid cooling of moltenmeta-toluylene diamineresults in'theformation of colloidal sizedparticles. Grinding of a material in a collo d mill in a suitable mediumcan also be used.

Atchesons process for thepreparation of colloidal graphite consists ofmechanical grinding of graphite in the presence of an agent, tannicacid, which prevents the agglrregationof the colloidal particles formedby grinding. The tannic acid functions as a protective agent and doesnot "materially ussist in the dispersion which is accomplished bymechanical action.

The distinction between dispersive and protective agents might be moreclearlyfillustrated as follows. Ponsol Blue is not oil in which itfirst'existed.

soluble and is diiiicult by ordinary means I i to incorporate this dyeinto an :oil medium-.1

A colloidalsolution of this dye is: made :in

water by any'suitable' method in the'presence. of an ammonium soap-WlllCll stabilizes or monium soap, there results a product which,

when ground in oil,again forms a colloidal solution but in a differentmediumthan that functions in the oil medium as-adispersive agent as wellas a protect ve agent.

As'many apparently widely diiferent bodiments of this invention may bemade.

without departing from the spirit-tliereof,it is 'to be understood thatwe do not limit ourselveszto theforegoing examples'or descriptionsexcept as indicated in the following patent'claims.

Weclaim: 1. ln'the method of uniformly: distribut ing compoundingingredients throughout a mass comprising coagulated' rubber, the stepsmass comprising rubber, the steps which comprise reducing'said compoundto particles of colloidal dimensions in the presence of a theingredients into. therubbe'r material.

The stearic' acid a whichcomprisethe formation; in a colloidal k systemof colloidal sized particlesof the comdispersing agent which 'i'ssolubleinrubber-at 1 thetemperature of milling, and introducing In themethod of uniformly distribut;

ing an anti-aging "compound throughouta mass comprising rubber, I thestepsu'lwhich compriselreducing the compound to particles of colloidaldimensions in the p'resen'cerof stearicaacidwhich is soluble in rubberat the temperature of milling, and introducing" the ingredients into therubber material.

a 4. In the process of preservinga cured rubber composition,.the stepswhich comprise producing a rubber preservingcompounding ingredient inthe-form ofparticles of colloidal dimensions in the presenceof a dis?persing and protectivev agent which is. soluble in rubber at thetemperature of milling, and

then introducing the prepared-ingredients into the rubber material. V

5. The process of claim t in which the dispersing and protective agent.is 'stearic acid. 6- The rubber product having incorporate ed tliereinan anti aging compound-which has-been reduced to particles of colloidaldi mensions in the presence of stearic EtClCh f I 7 A compoundingingredient for'frubber which comprises a system containing-inic'olrioloidal form an agent adapted toinhibit the deterioration of rubber and adispersing agent. which is soluble in rubber. .8. A compoundingingredient for rubber which comprises a colloidal system containing anagent adapted to inhibit the deterioration of rubber and stearic acid,said agent having been reduced to particles of colloidal dimensions inthe presence of the stearic acid. 9; Acompounding ingredient for rubberwhich comprises meta-toluylene diamine which has been reduced toparticles of colloidal dimensions in the presence of stearic acid.

10. A compounding ingredient for rubber which comprises-phenyl-alpha-naphthylamine and meta-toluylene-diamine which have beenreduced to particles of colloidal dimensions in the presence of stearicacid.

7 11. The rubber product having incorporated therein meta-toluylenediamine which has been reduced to particles of colloidal dimensions inthe presence of stearic acid. I 12. The rubber product havingincorporated therein phenyl-alpha-naphthylamine andmeta-toluylene-diamine which have been re- 'duced to particles ofcolloidal dimensions in the presence of stearic acid.

13. In the method of uniformly distributing meta-toluylene diaminethroughout a mass comprising coagulated rubber, the steps which comprisethe formation in a colloidal system of colloidal sized particles of themetaetoluyene diamine in the presence of an agent which tends topreserve the colloidal nature of the system and is soluble in rubber,

- and introducing the meta-toluylene diamine into the rubbermaterial. j

, 14. In the method of uniformly distributing meta-toluylene diaminethroughout a mass comprising rubber, the steps which com prise reducingsaid-meta-toluylene diamine to particles of colloidal dimensions in thepresence of a dispersing agent which is soluble in rubber at thetemperature of millin and introducing the meta-toluylene diamine intothe rubber material.

15. In themethod of uniformly distributing meta-toluylene diaminethroughout a mass comprising rubber, the steps which comprise-reducingthe meta-toluylene diamine to particles of colloidal dimensions in thepresence of stearic acid which is soluble in rubber at the temperatureof milling, and introducing the meta-toluylene diamine into the rubbermaterial.

16. In the method of uniformly distributing phenyl-alpha-naphthylamineand metatoluylene diamine throughout a mass comprising ,coagulatedrubber, the. steps which comprise the formation in a colloidal system ofcolloidal sized particles of the phenylalpha-naphthylamine andmeta-toluylene diamine in the presence of an, agent which tends topreserve the colloidal nature of the system and is soluble in rubber,and introducing the phenyl-alpha-naphthylamine and meta-toluylenediamine into the rubber material.

17.- In the method of uniformly distributing phenyl-alpha-naphthylamineand metatoluylene diamine throughout a mass com prising rubber, thestepswhich comprise reducing said phenyl-alpha-naphthylamine andmeta-toluylene diamine to particles of colloidal dimensions in thepresence of a'dispersing agent which is soluble in rubber at thetemperature of milling, and introducing the phenyl-alpha-naphthylamineand meta-toluylene diamine into the rubber material.

18. the method of uniformly distribute ing phenyl-alpha-naphthylamineand meta toluylene diamine throughout a masscomprising rubber, the stepswhich comprise reducing the phenyl-alpha-naphthylamine andmeta-toluylene diamine to particles of colloidal dimensions in thepresence of stearic acid which is soluble in rubber at the temperatureof milling, and introducing the phenyl-alpha-naphthylamine andmeta-toluylene diamine into the rubber material. l

In testimony whereof we affix our signa-

